Helicopters are used to great advantage in Search and Rescue (SAR) operations. A hoist is used in the helicopter to lower a rescue hook, a harness, a basket or other retrieval device at the end of a wire rope or cable, allowing the rescued person to be lifted up into the helicopter. Typically, the hoist is located above a door or other ingress/egress point on the helicopter, and positioned so that the rescued person is at the same level with the door when the wire rope is completely taken up.
The wire rope of the helicopter rescue hoist is typically wrapped tightly on a drum and is extended and retracted during operations. Hoist failures often occur when the hoist is run under no load and the wire rope becomes loose on the drum and fouls the rescue hoist mechanism. That is especially true when the hoist is operated on the ground during inspections and maintenance of the hoist and wire rope. During inspection and maintenance, the wire rope is often unprotected and slack in the wire rope can result in damage to the wire rope and the rescue hoist. If the hoist wire rope loosens, significant damage to the hoist can result. Miswraps of the wire rope on the hoist drum due to loosening of the wire rope can foul the hoist in flight putting the crew and mission in jeopardy.